Atomic-Scale Insights into the Temperature-Dependent Oxidation of SiC and Si3N4 Ceramics: A Molecular Dynamics Study

Thermal oxidation of silicon-based coatings is the focus of attention in their application at high temperature, especially for SiC and Si3N4 coatings. Even though understanding and unveiling the oxidation degree of such silicon-based coatings are important to improve the application value of their outstanding ability at high temperature performance, insights into the oxidation mechanism are unclear at the atomic scale. Here, we investigate the initial oxidation behavior of SiC and Si3N4 with molecular dynamics simulations. Oxidation processes of different polytypes of SiC and Si3N4 with respect to various orientations in an oxygen atmosphere are simulated at typical temperatures ranging from 500 to 1800 K within 200 ps in order to provide further development of new ceramic coatings, which is expected to predict the effect of temperature on the oxidation of SiC and Si3N4. The oxidation of nonpolar 6H-SiC (001) and β-Si3N4 (001) surfaces as typical surfaces is focused on to study the differences between SiC and Si3N4. Our studies demonstrate that the oxidation of Si3N4 is more sensitive to temperature than that of SiC because diffusion of O atoms into β-Si3N4 (001) substrate is more intense than that into 6H-SiC (001).